1. Field of the Invention
The present invention is directed to a shock wave source, particularly a lithotripter, having an ultrasound generator for generating a pressure wave which can be focussed to disintegrate or shatter calculi in a patient.
2. Description of the Prior Art
A lithotriper having an ultrasound generator resonator or vibrator which generates a pressure pulse and which has an approach or transmission path through which the pressure wave passes in the direction toward a patient thereby forming a "shock wave" is disclosed in German Pat. No. OS 31 19 295. In this known device, a plurality of ultrasound transducer elements are used which emit a focussed pressure wave either electronically or mechanically (by shaping). The approach path, through which the pressure wave passes, is disposed between the transducer elements and the patient, and is coupled to the patient so as to form the shock wave inside the patient for destroying calculi. The approach path is this known device is filled with water.
Piezoceramic transducer elements are preferably used in such a shock wave source. A disadvantage of piezoceramic transducer elements, however, is that a relatively steep pressure pulse is generated by the pressure source, and thus transition or "steepening" of such pressure pulse into a "shock wave" takes place relatively early, i.e., at an undesirable large distance from the focus. This is undesirable because a "shock wave," as compared to the pressure pulse, has considerable additional attenuation associated therewith due to non-linear effects. In water, such non-linear attenuation is much greater than normal linear attenuation. The resulting "shock wave" thus loses considerable energy before reaching the focus, at which the calculus to be disintegrated is isolated. Moreover, the extremely short pulse duration of the "shock wave" results in an extremely short wavelength of the fundamental oscillation. A very small focus zone, with a correspondingly small effective volume, thereby results for the disintegration of the calculus.